Drill bit stabilizer

ABSTRACT

A stabilizer for a drill string and drill bit is mounted behind the drill bit in the drilling assembly. The stabilizer comprises a tubular body having one or more stabilizer blades mounted thereon. The stabilizer blades extend radially outwardly from the stabilizer body. In a first position, the stabilizer blades are in vertical axial alignment behind the drill bit. Drill string pressure is utilized to release a locking mechanism permitting relative rotation between the stabilizer blades and the stabilizer body thereby rotating the stabilizer blades to a second position providing stabilization for the drill string and drill bit.

BACKGROUND OF THE DISCLOSURE

[0001] The present invention relates generally to drill bit stabilizers for drilling subterranean formations, particularly, to a stabilizer for providing full gauge stabilization for a drill bit.

[0002] When drilling a well bore, for example drilling an oil and gas well, many problems are encountered. A substantial portion of such drilling problems relate to drill bit and drill string instability which places high stress on drilling equipment, not only on drill bits but also on downhole tools and the drill string. Drill bit instability problems are particularly inherent with bi-center bit designs because of an inability to provide full gauge stabilization near the bit. Bi-center bits drill a larger hole than the pass through diameter of the casing, therefore conventional stabilizers cannot pass through the casing with the bi-center bit. For this reason, bi-center bits are typically run with no stabilization within approximately the bottom 50 feet of the borehole assembly. Bi-center drill bits, designed to simultaneously drill and under-ream a wellbore, are particularly prone to poor directional control, and often produce smaller than expected hole diameter because of the lack of stabilization. While bi-center bits have been available for more than twenty years, they have seen limited use because of the inherent problems associated with bi-center drill bits. New technologies however have led to the design of new bi-center bits which perform comparable to conventional drill bits.

[0003] Bi-center bits are now in greater demand for use in various drilling applications, including directional drilling in deep water where using a steerable motor assembly is necessary. Current bi-center bit designs focus on minimizing bi-center force imbalance. While advances have been made to overcome the inherent instability of the bi-center bit, it has yet to realize its full potential as a reliable alternative to conventional undereaming.

[0004] It is therefore an object of the present invention to provide a stabilizer for providing drill bit directional control and engagement with the borehole wall.

[0005] It is another object of the present invention to provide a bi-center drill bit stabilizer mounted behind the bi-center bit. In a first position, the stabilizer blade of the invention is positioned axially aligned with the reamer wing of the bi-center bit.

[0006] It is yet another object of the present invention to provide a drill bit stabilizer which may rotationally deploy a stabilizer blade from a first position to a second position opposite the first position.

[0007] It is still another object of the invention to provide a stabilizer apparatus providing full gauge stabilization.

[0008] It is a further object of the invention to provide full gauge stabilization for a drilling apparatus in a borehole.

SUMMARY OF THE INVENTION

[0009] The present invention provides a stabilizer for a drill bit. The stabilizer is mounted behind the drill bit in the drilling assembly. The stabilizer comprises a tubular body having one or more stabilizer blades mounted thereon. The stabilizer blades extend radially outwardly from the stabilizer body. In a first position, the stabilizer blades are in axial alignment behind the drill bit. Drill string pressure is utilized to release a locking mechanism permitting relative rotation between the stabilizer blades and the stabilizer body thereby rotating the stabilizer blades to a second position providing stabilization for the drill bit.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] So that the manner in which the above recited features, advantages and objects of the present invention are attained can be understood in detail, a more particular description of the invention briefly summarized above, may be had by reference to the embodiments thereof which are illustrated in the appended drawings.

[0011] It is noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.

[0012]FIG. 1 is a side view of the stabilizer of the invention;

[0013]FIG. 2 is a section view of the stabilizer of the invention depicting the stabilizer with a single stabilizer blade;

[0014]FIG. 3 is a section view of the stabilizer of the invention taken along line 3-3 of FIG. 2;

[0015]FIG. 4 is a side view of the stabilizer of the invention illustrating the stabilizer of the invention mounted behind a bi-center bit being lowered in a borehole;

[0016]FIG. 5 is a side view of the stabilizer of the invention illustrating the location of the stabilizer in a second position providing drill bit stabilization;

[0017]FIG. 6 is a side view of an alternate embodiment of the stabilizer of the invention;

[0018]FIG. 7 is a section view of the stabilizer of the invention shown in FIG. 6;

[0019]FIG. 8 a is section view of the stabilizer of the invention taken along line 8-8 of FIG. 7;

[0020]FIG. 9 is a section view of the stabilizer of the invention taken along line 9-9 of FIG. 7; and

[0021]FIG. 10 is a side view of the stabilizer of the invention depicting the stabilizer blades in a full gauge position.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

[0022] Referring first to FIG. 1, the stabilizer of the invention is generally identified by the reference numeral 10. The stabilizer 10 of the invention includes a substantially tubular body 12, manufactured from steel or other hard metal material. A threaded pin 14 is provided at one end of the stabilizer body 12 for connection to a drill string 13 located in a borehole 15, as best shown in FIG. 4. The opposite end of the stabilizer body 12 is provided with a threaded coupling 16 for connection to a drill bit 17. A stabilizer blade 18 integrally formed on a cylindrical collar 20 is mounted on the stabilizer body 12. The blade 18 extends radially outward from the collar 20 which includes an axial passageway for receiving the pin end of the stabilizer body 12 therethrough. The collar 20 is positioned about the central portion and rests against the shoulder 21 of the stabilizer body 12 as best shown in FIG. 2.

[0023] Referring still to FIG. 2, the circumferential shoulder 21 is formed on the external surface of the stabilizer body 12. The shoulder 21 provides a stop or support surface for engagement with the lower end of the collar 20. A sleeve 22 secured about the upper portion of the stabilizer body 12 engages the upper end of the collar 20 for retaining the collar 20 on the stabilizer body 12. The sleeve 22 is secured to the stabilizer body by a lock key 24 which extends through an opening in the side of the sleeve 22 and is received in a recess formed in the stabilizer body 12. The key 24 is fixedly secured in position by a bolt 26 or similar connector.

[0024] The collar 20 and stabilizer blade 18 are retained on the stabilizer body 12 between the shoulder 21 and the sleeve 22 which prevent relative axial movement between the stabilizer body 12 and the collar 20. Relative rotational movement, however, between the stabilizer body 12 and the collar 12 is permitted.

[0025] Referring now to FIGS. 2 and 3, an axial passage 28 extends through the stabilizer body 12. An actuator piston housing 32 is located within the passage 28 as best shown in FIG. 2. The piston housing 32 is cylindrical in shape having an external diameter substantially equal to the diameter of the passage 28 below a circumferential shoulder 30 formed on the internal surface of the stabilizer body 12. The piston housing 32 is positioned within the passage 28 so that its planar end surface 33 is in facing contact with the internal circumferential shoulder 30. O-rings 35 received in circumferential recesses formed adjacent to the upper and lower ends of the piston housing 32 form a seal between the periphery of the piston housing 32 and the internal surface of the stabilizer body 12 defined by the passage 28. A pair of passages 37 extend through the piston housing 32 permitting drilling fluid to pass therethrough.

[0026] The piston housing 32 includes a transverse passageway 34 proximate to the end surface 33 of the piston housing 32. The passageway 34 is sized to receive a piston rod 36. Load pins 38 and 40 are mounted on the ends of the piston rod 36. The pins 38 and 40 are received in recesses 39 and 41, respectively, formed in the stabilizer body 12. Shoulder screws 42 extend through the pins 38 and 40 and secure the pins 38 and 40 to the distal ends of the piston rod 36.

[0027] Referring now specifically to FIG. 3, the pin 38 is provided with a neck portion 44 which depends from the bottom surface 63 of the pin 38. A spring 46 is journalled about the neck 44 of the pin 38. The spring 46 is retained in the recess 39 between the bottom surface 63 of the pin 38 and an inwardly extending circumferential shoulder 48 which defines the bottom of the recess 39. The spring 46 exerts an outward force against the bottom of the pin 38 so that the leading edge of the pin 38 projects beyond the periphery of the piston housing 32 into a circumferentially extending recess 45 formed in the inner wall of the collar 20. One side of the pin 38 includes a planar surface 53 offset from and parallel to the cental axis of the load pin 38. In the initial or start position shown in FIG. 3, the surface 53 of the pin 38 is in facing contact with a wall 47 defining one end of the recess 45. The opposite end of the recess 45 is defined by a wall 49 diametrically opposite the wall 47.

[0028] The outwardly biasing force of the spring 46 is aided by the borehole pressure which is transmitted to the piston rod 36 through a fluid conduit 55 formed in the body of the piston housing 32. The conduit 55 is in fluid communication with a passage 57 extending through the wall of the stabilizer body 12 and is open to the borehole 15. Thus, borehole pressure is transmitted to a fluid chamber 61 about a portion of the piston rod 36 via the passage 57 and conduit 55 adding redundancy to the biasing force applied to the pin 38 by the spring 46.

[0029] Referring still to FIG. 3, a brake shoe 50 is pivotally mounted on the periphery of the blade 18. The shoe 50 is secured in a recess 51 formed in the blade 18 by a pivot pin 52. Radial movement of the shoe 50 is limited by a pin 54 mounted in the blade recess 51 and extending through a slot 56 formed through the shoe 18. A spring 58 retained in bore 60 formed in the blade 18, urges the shoe 50 outwardly as shown in FIG. 3. As the stabilizer 10 rotates in the borehole 15 with the drill bit 17, the outward force applied by the spring 58 and centrifugal force developed by the rotating stabilizer 10 forces the shoe 50 radially outwardly about the pivot pin 52 into engagement with the wall of the borehole 15.

[0030] Referring now to FIG. 4, the stabilizer 10 of the invention is shown used in combination with a bi-center bit 17. It will be observed that unlike most drilling tools, the center axis of the bit 17 and stabilizer 10 while being lowered or tripped in the casing or borehole 15 is not the same as the borehole axis. The stabilizer 10 is mounted behind the bit 17 so that the blade 18 is above and aligned with the reamer wing 62 of the bit 17. It will further be observed that the maximum diameter of the bi-center bit 17 is greater than the diameter of the pilot bit 64 mounted on the lower or face end of the bit 17. In this configuration, the stabilizer 10 and bit 17 offset to one side of the casing or borehole 15 when tripped in so that they fit inside the borehole 15 as shown in FIG. 4. Once drilling commences, the pilot bit 64 centralizes the drill string assembly, including the stabilizer 10 and the drill bit 17, thereby causing the reamer wing 62 and the stabilizer blade 18 to rotate about the borehole axis and thus increase the diameter of the borehole 15 below the casing as shown in FIG. 5.

[0031] As drilling begins, the stabilizer blade 18 is oriented in the same direction as the reamer wing 62 as shown in FIG. 4. When the drill string pressure in the passage 28 exceeds a predetermined value, a burst plate 66 covering the lower end of a second conduit 68 provided in the piston housing 32 bursts, thereby providing a fluid passage to the fluid chamber 69 formed about a portion of the piston rod 36 so that the fluid pressure in the passage 28 is applied against the piston rod 36.

[0032] The drill string fluid pressure in the passage 28 is greater than the borehole pressure. Thus, the higher pressure in the chamber 69 applied against the piston rod 36 forces the piston rod 36 to move to the left in the view shown in FIG. 3. Retraction of the pin 38 into the recess 39 compresses the spring 46 and disengages the piston surface 53 from the wall 47 permitting the stabilizer body 12 to rotate relative to the stabilizer blade 18 and collar 20. Rotation of the stabilizer body 12 allows the pin 40 to moive to the position of the pin 38 shown in FIG. 3 into engaging contact with the wall 47 of the recess 45. The stabilizer body 12 and the bit 17 connected thereto rotate 180° so that the reamer wing 62 is opposite the stabilizer blade 18 as best shown in FIG. 5.

[0033] In the configuration shown in FIG. 5, the stabilizer blade 18 and the reamer wing 62 project in opposite directions in the borehole 15. When drilling is completed and circulation is stopped, fluid pressure in the chambers 61 and 69 on both sides of the piston rod 36 is equalized permitting the spring 46 to force the pin 38 outward and thereby disengage the pin 40 from the wall 47 of the recess 45. The stabilizer body 12 is then rotated to its original position locating the stabilizer blade 18 behind the reamer wing 62 so that the bit 17 may be removed from the borehole 15.

[0034] Referring now to FIGS. 6-10, an alternate embodiment of the invention providing full gauge borehole stabilization is disclosed. The full gauge stabilizer is generally identified by the reference numeral 100. The stabilizer 100 is substantially similar to the stabilizer 10 described above. Therefore, the same reference numerals are used to identify like components.

[0035] The stabilizer 100 provides full gauge stabilization behind the drill bit 17. That is, the stabilizer 100 contacts the borehole wall at three point approximately 120° apart. The stabilizer 100 includes a stabilizer body 102 substantially similar to the stabilizer body 12 shown in FIG. 2, but longer in length for supporting three stabilizer blades stacked one above the other. Beginning at the lower end of the stabilizer body 102, the lowermost stabilizer blade 104 is integrally formed with the stabilizer body 102. It extends outwardly from the stabilizer body 102 in the same manner as the stabilizer blades 18 but does not include a brake shoe 50. The stabilizer blade 104 rotates with the stabilizer body 102 as will be described in greater detail hereinafter.

[0036] Referring now to FIG. 7, a pair of stabilizer blade assemblies 106 and 108 are mounted on the stabilizer body 102 in vertical alignment above the stabilizer blade 104. The blade assemblies 106 and 108 are substantially identical to the blade assembly of the embodiment of the invention shown in FIGS. 1-5 and described herein. Thrust bearings 1 10 and 1 12 are provided to reduce binding between the stabilizer blade assemblies 106 and 108 and the stabilizer body 102.

[0037] The stabilizer 100 is tripped in the borehole 15 in the same manner described above. The stabilizer blades are aligned above the reamer wing 62 of the bi-center bit 17 permitting the bi-center bit and stabilizer 100 to move to one side of the borehole 15. When the bottom of the borehole 15 is reached and the drill string is rotated, the pilot bit 64 centralizes the assembly so that the reamer wing 62 rotates about the central axis of the borehole 15. The center of the bi-center bit 17 thus becomes the center of the borehole 15 allowing the reamer wing 62 and pilot bit 64 to enlarge the borehole 15 to the desired diameter.

[0038] Referring again to FIG. 7, it will be observed that the fluid conduits 55 and 68 of the piston housings 32 of the blade assemblies 106 and 108 are vertically aligned so that fluid pressure from the borehole 15 and the lower portion of the axial passage 28 extending through the stabilizer body 102 is communicated to the piston rod 36. In the manner previously described, upon reaching a predetermined fluid pressure value in the passage 28, the burst plate 66 bursts and the drill string pressure is communicated to piston rods 36 of the stabilizer assemblies 106 and 108. The increase in fluid pressure actuates the piston assemblies forcing the pin 38 in the stabilizer assembly 106 to retract and disengage from the wall 112 of a circumferentially extending recess formed in the collar 20, thereby permitting the drill bit 17, the stabilizer body 102, the stabilizer blade 104 and the stabilizer assembly 108 to rotate relative to the stabilizer assembly 106. Assuming that the blade 18 of the stabilizer assembly 106, in the orientation shown in FIG. 7, defines the 0° point about the borehole 15, the stabilizer assembly 108 rotates 120° about the central axis of the borehole 15. The stabilizer body 102 and blade 104 rotate 240° about the central axis of the borehole 15. The relative rotation between the components is limited by the engagement of the pins 40 against the wall 114 of a circumferential recess 116 formed in the collar 20 of the stabilizer assembly 106 and the wall 118 of a circumferential recess 120 formed in the collar 20 of the stabilizer assembly 108. The position of the stabilizer blade 104 and the blade 18 of the stabilizer assembly 108 is shown in phantom in FIG. 9. Thus, the stabilizer blades 18 and 104 contact the borehole wall at three points about the central axis of the borehole 15 approximately 120° apart, thereby providing full gauge stabilization of the drill string behind the bit 17.

[0039] While several preferred embodiments of the invention have been shown and described, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims which follow. 

1. A drill bit stabilizer, comprising: a) a stabilizer body having an axial passage extending therethrough, said stabilizer body including a pin connector on one end and a box connecter on the other end for connecting said stabilizer body in a drill string; b) at least one stabilizer blade mounted about said stabilizer body; c) an actuator housing mounted in said axial passage of said stabilizer body; d) piston means carried by said housing for coupling said stabilizer blade with said stabilizer body; and e) conduit means providing fluid communication between said piston means and said axial passage of said stabilizer body.
 2. The apparatus of claim 1 wherein said piston means comprises a piston rod having pins mounted on the distal ends thereof, and wherein said piston rod and said pins are in a transverse bore extending through said actuator housing and said stabilizer body.
 3. The apparatus of claim 1 including means pivotally mounted on the periphery of said stabilizer blade for engaging the inner wall of a borehole upon rotation of said stabilizer body.
 4. The apparatus of claim 3 wherein said pivotal means comprise a brake shoe mounted in a recess formed on the peripheral edge of said stabilizer blade.
 5. The apparatus of 4 wherein said brake shoe is pivotally secured in said recess and further including biase means providing an outward force against said brake shoe.
 6. The apparatus of claim 4 wherein said brake shoe includes an axial elongate slot and a post extending through said slot and secured in said recess for limiting the outward radial movement of said brake shoe.
 7. The apparatus of claim 1 including means for rotating said stabilizer body relative to said stabilizer blade from a first position to a second position.
 8. The apparatus of claim 1 including at least three stabilizer blades vertically aligned on said stabilizer body.
 9. The apparatus of claim 8 wherein one of said stabilizer blades is integrally formed with said stabilizer body.
 10. The apparatus of claim 8 wherein said stabilizer blades are rotated from a first position to a second position for providing full gauge stabilization. 